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Vacuum Drying in a Bag

Started by Glen Evans, February 09, 2005, 12:53:00 PM

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Den Socling

isimitibiti (Tyler) was here this afternoon. He wants to build a discontinuous vac now. He said the bag was working but it's time to move up.

I asked him a half dozen times to get back in here and pass 'bag-vac technology' along to you wood turners and guys after one dry slab. Hope he does. Also would be nice if he shares his discontinuous vac experience.

Ironwood

Someone out there has a patent on a bag vaccum drying process.(I won't say anything else) It is possible. Reid
There is no scarcity of opportunity to make a living at what you love to do, there is only scarcity of resolve to make it happen.- Wayne Dyer

Den Socling

Reid,

That's Zhangjing Chen with the patent. He's a friend of mine. Just don't try to market a system using a bag without his involvement.

Den

PS There are patents for steam vacs, also.

Ironwood

Den,

  Unless he bought it from the guy I know (several offers were tendered but not accepted) it is a differing patent. It is an international patent. Reid
There is no scarcity of opportunity to make a living at what you love to do, there is only scarcity of resolve to make it happen.- Wayne Dyer

Den Socling

Hi Reid,
I almost have an world patent. Its a long, long process. They investigate the dickens out of them. Mine has been going on for a year or more and is suppose to be final in the 'first half' of this year. If a similar patent exist in a country that signed the WIPO treaty, a world patent doesn't happen. I've read Chen's patent and it is current. Chen is a researcher at Virginia Tech @ Blacksburg with Fred Lamb.
Den

Ironwood

Den,

Fred is a nice guy. I spoke with him for what seemed like hours a few years back about my project. He was very helpful and at the time informed me of some federal grant monies available for my application, it was just too much regulation for me and I didn't see it benefiting me that much. Great guy, definitely one of the vac. gurus.

                                Reid
There is no scarcity of opportunity to make a living at what you love to do, there is only scarcity of resolve to make it happen.- Wayne Dyer

iain

I talked today Ian Holmes of Becker pumps UK,

his pumps will run 24-7 for years doing this job, his advice to anyone (when i splaned what we wanted to do and the problems)
use pumps that will run at 60c or above and that stops the moisture condensing into the oil it gets passed straight out as exhaust

sounds like a plan to me for when i get to the new work shop,


here's the link for north Americadia

http://www.beckerpumps.com/


iain

Den Socling

In the systems that I have seen running oil, some oil goes out with the pump discharge and that makes a real mess. One company in PA had a 'dead zone' outside the factory where they were discharging. Another company in NY was told by their 'EPA' to change to water or shut down. Oil might work if you used some way of catching the oil mist.

logboy

I've been looking into the bag technique for drying hardwood slabs for a while.  Did anyone ever follow up on it? Where are the bags from? What is the rough setup?
I like Lucas Mills and big wood.  www.logboy.com

Den Socling

I believe the idea can work. Vacuum storage bags may be suitable but I don't know how big they go.

logboy

Do you know what isimitibiti was using?
I like Lucas Mills and big wood.  www.logboy.com

Den Socling

No I don't know what he used but a "chamber" might be made from plastic sheathing with duct taped seems. The tricky part would be the connection for the pump.

logboy

I dont think the bags or the connection would be an issue as long as one of these would work. The down side would be the "softening point" of 150 degrees. The hot box would need to be kept below that temp.  What kind of vacuum

http://www.veneersupplies.com/categories/Vacuum__Press__Items/Vacuum__Bags__%26__More/Dura-Max__Extreme%E2%84%A2__Vacuum__Bags/
I like Lucas Mills and big wood.  www.logboy.com

Den Socling

Those bags look like they might fit the bill. But odd sizes. Too big.

Many species will reach 7% at 140'F. A couple, like Black Walnut burl, needs 180'F.

I usually run the vacuum around 55 Torr (55mm Hg). A chamber pressure of 65 will work. If you go above 65, the boiling point (and wood temperature) goes above 110'F.

logboy

I was checking over your chart and 65 Torr correlates  to 109 degrees F. So theoretically with a "chamber" temp of 125 the wood would be at the required temp and yet still not soften the bags.

What kind of vacuum pump would be necessary to correctly run this setup? I kept reading about oil/water mixture problems. Is a different pump the solution, or a condenser of some sort?
I like Lucas Mills and big wood.  www.logboy.com

Den Socling

If your wood is wet, evaporation keeps the temperature at a level set by chamber pressure. So, if you have 65 Torr, the wood can't go above 110. If you were heating in a bath of 125, the extra energy would speed up drying.

I use shell and tube heat exchangers as condensers. I use liquid ring vacuum pumps because they can take some water if any gets past the condenser. There are dry, screw pumps but they cost two or three times that of liquid ring. The thing about drying in a bag is that a tiny pump would do.

logboy

If I am reading right from the other posters the pump would not need to be run continuously either. Some sort of small pump hooked up to a basic timer in a thermostat controlled hot box might do the trick.
I like Lucas Mills and big wood.  www.logboy.com

Den Socling


JasonRerras

Can anyone recommend a liquid ring vacuum pump?  Can these be had for a couple hundred dollars or is it going to be several thousand?

Alternatively, would an cheap automotive A/C vacuum pump (ala harbour freight) work as a more temporary solution assuming you could effectively condense the water before the pump??

 I have a number of slabs that are air dried, and it would be nice to be able to kiln dry them one at a time as needed. 

I've searched all over this forum and google, and this thread seems to be the only info I can find.



MS880 60" CSM and stuff

btulloh

I use a Robinair pump that was intended for HVAC service work.  It works fine and I got it used for a couple hundred dollars.  With any of these, you probably need to build a vacuum reservoir and put a vacuum switch and unloader valve in the plumbing.  Those pumps are not designed to run continuously.  I found a general design somewhere on the web - maybe one of the woodworking magazines.  It was probably 15 years ago.

 I don't use it for drying, I use it for vacuum bag glue ups.
HM126

JasonRerras

Thanks, the unloader takes the load off the pump after the bag had reached vacuum, right?
MS880 60" CSM and stuff

btulloh

The unloader just allows the pump to be able to start again.  Same as with a compressor.  Maybe it's called a MAC valve in a vacuum situation.  It was quite a few years ago when I built the thing.

Here's a source of supplies:  

Vacuum Press Parts - Build Your Own and Save

This is similar to the design I used:

Do-It-Yourself Vacuum Veneer Press

Mine was for a vacuum press, so I don't really know how that applies for your task, but pulling a vacuum for an extended time is all about the same.  You may have to do something about the moisture that is coming out, but I think the HVAC vacuum pump handles that ok.  I'm not an expert, I just learned enough to get the vacuum press working, and it's been fine for 15 years.
HM126

JasonRerras

Thanks for the info.  The moisture is the big issue as there will be gallons coming out, and you definitely need a condenser to capture the water vapor before the pump.  Looks like one can get a used liquid ring pump for a little more than an conventional pump, and that will tolerate the moisture much better while still using a condenser.
MS880 60" CSM and stuff

Don P

Far from knowing but I think moisture is why the HVAC guys are always changing the oil in those.

btulloh

Sounds about right.  Oil doesn't improve much  when you mix it with water . I guess that's where the condenser comes into play.  I haven't needed to chainge the oil, but I'm not dealing with much moisture in a press.  

I'll be curious to see how this turns out.  
HM126

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